Diabetes Mellitus is a disorder of the carbohydrate metabolism characterized by abnormal insulin secretion. Depending upon the degree of insulin secretion impairment, diabetics are classified as either ketoacidosis-prone or ketoacidosis-resistant. These classifications are also known as juvenile-onset or insulin-dependent and maturity-onset or non-insulin dependent, respectively. In some cases, insulin-dependent or ketoacidosis-prone diabetics are difficult to manage. Such patients are often called "brittle" diabetics and occasionally such patients must be hospitalized in order to determine their insulin requirements and in effect stabilize their condition.
Even in the above situation where a patient is hospitalized and/or subsequently stabilized, the long-term results of such abnormal insulin/glucose blood levels are serious physical impairments such as retinapathy, neuropathy and other serious clinical manifestations.
In the past, screening methods such as the determination of the presence of abnormal levels of glucose and ketone-bodies in the urine were also used to monitor the condition of the status of control of diabetic patients. Such methods were used because of the availability of simplified test reagents such as paper strips impregnated with reagents and the non-invasive nature of the urine sample being tested. Such methods are very unsatisfactory since by the time the glucose spills over into the urine, the patient is usually well out of control.
More recently, methods have been developed which involve the determination of glucose levels in blood as a measure of the status of control of a diabetic patient. Such methods initially involved laboratory procedures since the tests were conducted using plasma rather than whole blood. However, in the past two to three decades, methods have evolved using reagent strips which can be used with small amounts of whole blood, such as from droplettes of whole blood taken from a finger-tip puncture with a sterile lancet. Such methods, coupled with a simple, battery operated reflectance meter have opened entirely new testing vistas and have led to the concept of home testing by the diabetic himself. Thus, several tests can be conducted in a single day without unduly inconveniencing the patient and the attending physician.
Regardless of the above advances, present methods for assessing or monitoring the status of control of brittle diabetics is far from ideal. This is partially due to the fact that blood glucose levels may vary widely during the course of a few hours or less due to varying sugar intake and varying ability to metabolize glucose. Frequent blood glucose measurements are recommended. A simple blood sample provides only limited information regarding the success of the patient in controlling glucose levels. A single point glucose measurement provides limited information. FIG. 1 provides a hypothetical graph of blood glucose levels during the course of a day. Samples taken only at times t.sub.b, t.sub.d and/or t.sub.f might erroneously suggest that the hypothetical patient in FIG. 1 is adequately controlled. Sampling at more frequent intervals, for example at time t.sub.a through t.sub.g inclusive, would yield a more complete picture suggesting that the patient is not well controlled at all, but in fact is cycling through high and low serum glucose levels during the course of the day. A patient may require that as many as eight or more blood samples be drawn daily in order that an adequate picture of blood glucose levels be obtained. Obtaining blood samples is an invasive process which is usually neither pleasant nor convenient. A means of obtaining additional information from a single blood sample which would either reduce the total number of samples needed to be drawn or allow for a clearer clinical picture to be drawn from such determinations would clearly be beneficial and valuable to the patient.
More recently, a method has been developed which overcomes some of the above noted testing deficiencies. This new method is based on the finding that the glycosylated fractions of hemoglobin A (HbA) are increased in diabetics in proportion to the level of elevation of blood glucose above normal. The glycosylated or "fast" hemoglobins are formed continuously in the red cell over its 120-day life span and it was found that the amount of the most abundant fraction HbA.sub.lc may double in diabetics which have not been adequately controlled over the period during which this fraction is formed. Thus a test for the determination of HbA.sub.lc is indicative of how well a diabetic has been controlled during the previous several months.
This test, although an advance in the art, is not entirely satisfactory since it is a complicated laboratory test and information is not obtained on a timely basis, i.e., the information is obtained only after about 2-3 months during which the diabetic may be considerably out of control and suffering the impairments described herein.